This may seem like a pitiful return on the investment, especially if you compare it to the hundreds of pounds of moon rocks returned by the Apollo astronauts. But the Stardust spacecraft also came back to Earth with little more than microscopic particles from Wild 5's coma, so this is not a wholly disappointing sampling (indeed, in light of Hayabusa's troubles, JAXA will be relieved to find anything inside). So long as there's enough material available to study, this will be deemed a success.